The present invention relates to a new and distinctive cucumber inbred line, designated 8D-5079. There are numerous steps in the development of any novel, desirable plant germplasm. Plant breeding begins with the analysis and definition of problems and weaknesses of the current germplasm, the establishment of program goals, and the definition of specific breeding objectives. The next step is selection of germplasm that possess the traits to meet the program goals. The goal is to combine in a single variety or hybrid an improved combination of desirable traits from the parental germplasm. These important traits may include higher yield, field performance, fruit and agronomic quality such as fruit shape and length, small cavity size, flesh texture, resistance to diseases and insects, and tolerance to drought and heat.
Practically speaking, all cultivated forms of cucumber belong to the highly polymorphic species Cucumis sativus L. that is grown for its edible fruit. As a crop, cucumbers are grown commercially wherever environmental conditions permit the production of an economically viable yield. They can be hand or mechanically harvested. Cucumbers that are grown for fresh market, also called slicers, are generally hand harvested. Those that are to be processed are called pickles and may be hand or mechanically harvested. They are produced on trailing or climbing vines. On healthy plants there is a canopy of large, regular, three lobed leaves, in an alternate arrangement. Pickling cucumbers grown in the United States have usually blunt and angular fruits. They are white-spined and most possess dark green or medium dark green exterior color. Most slicers have slightly rounded ends and taper slightly from the stem to blossom end, although cylindrical-shaped fruits with blocky or even rounded ends are also available. Many changes that occurred with the domestication of the cucumber relate to fruit morphology, with a specialization in fruit shape and size. Slicing cucumbers are frequently sold in lengths from 6 to 10 in. and diameter varies from 11/2 to nearly 3 in. In the United States, the principal slicer cucumber growing regions are Georgia, Florida, Michigan, California and North Carolina with nearly 42,000 acres out of a US total acreage of 57,500 acres. The main states that produce processing cucumbers are Michigan, North Carolina and Texas. Fresh cucumbers are available in the United States mainly from spring to fall. Cucumbers are consumed in many forms, generally processed for pickling types and as fresh market product for slicers. Although slicing cultivars may be processed, they generally are not acceptable substitutes for the pickling cucumbers.
Cucumis sativus is a member of the family Cucurbitaceae. The Cucurbitaceae is a family of about 90 genera and 700 to 760 species, mostly of the tropics. The family includes melons, pumpkins, squashes, gourds, watermelon, loofah and many weeds. The genus Cucumis, to which the cucumber and several melons belong, includes about 70 species. The cucumber is believed to be native to India or Southern Asia and has been apparently there for 3000 years.
Cucumber is distinct from other Cucumis species in that it has seven pairs of chromosomes (2n=2x=14) whereas most others have twelve pairs or multiple of twelve. Pollination techniques for controlled crosses in cucumbers are easy to conduct. If bees and natural pollen vectors can be excluded, the breeder need not to be concerned about preventing selfing or other pollen contamination because of the diclinous nature of cucumbers and the stickiness or adherence of pollen to its source flower. There is no wind dissemination of pollen. Pistillate flowers are receptive in the morning or up to midday on the day they open. Cucumbers have a broad range of floral morphologies, from staminate, pistillate to hermaphodite flowers, yielding several types of sex expression.
Choice of breeding or selection methods depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the type of cultivar used commercially (e.g., F1 hybrid cultivar, pureline cultivar, etc.). For highly heritable traits, a choice of superior individual plants evaluated at a single location will be effective, whereas for traits with low heritability, selection should be based on mean values obtained from replicated evaluations of families of related plants. Popular selection methods commonly include pedigree selection, modified pedigree selection, mass selection, and recurrent selection.
The complexity of inheritance influences choice of the breeding method. Backcross breeding is used to transfer one or a few favorable genes for a highly heritable trait into a desirable cultivar. This approach has been used extensively for breeding disease-resistant cultivars. Various recurrent selection techniques are used to improve quantitatively inherited traits controlled by numerous genes. The use of recurrent selection in self-pollinating crops depends on the ease of pollination, the frequency of successful hybrids from each pollination, and the number of hybrid offspring from each successful cross.
Each breeding program should include a periodic, objective evaluation of the efficiency of the breeding procedure. Evaluation criteria vary depending on the goal and objectives, but should include gain from selection per year based on comparisons to an appropriate standard, overall value of the advanced breeding lines, and number of successful cultivars produced per unit of input (e.g., per year, per dollar expended, etc.).
Promising advanced breeding lines are thoroughly tested and compared to appropriate standards in environments representative of the commercial target area(s) for three years at least. The best lines are candidates for new commercial cultivars; those still deficient in a few traits are used as parents to produce new populations for further selection.
These processes, which lead to the final step of marketing and distribution, usually take from eight to 12 years from the time the first cross is made. Therefore, development of new cultivars is a time-consuming process that requires precise forward planning, efficient use of resources, and a minimum of changes in direction.
A most difficult task is the identification of individuals that are genetically superior, because for most traits the true genotypic value is masked by other confounding plant traits or environmental factors. One method of identifying a superior plant is to observe its performance relative to other experimental plants and to a widely grown standard cultivar. If a single observation is inconclusive, replicated observations provide a better estimate of its genetic worth.
The goal of plant breeding is to develop new, unique and superior cucumber inbred lines and hybrids. The breeder initially selects and crosses two or more parental lines, followed by repeated selfing or sib crossing and selection, producing many new genetic combinations. The breeder can theoretically generate billions of different genetic combinations via crossing, selfing and mutations. The breeder has no direct control at the cellular level. Therefore, two breeders will never develop the same line, or even very similar lines, having the same cucumber traits.
Each year, the plant breeder selects the germplasm to advance to the next generation. This germplasm is grown under unique and different geographical, climatic and soil conditions, and further selections are then made, during and at the end of the growing season. The inbred lines that are developed are unpredictable. This unpredictability is because the breeder""s selection occurs in unique environments, with no control at the DNA level (using conventional breeding procedures), and with millions of different possible genetic combinations being generated. A breeder of ordinary skill in the art cannot predict the final resulting lines he develops, except possibly in a very gross and general fashion. The same breeder cannot produce the same line twice by using the exact same original parents and the same selection techniques. This unpredictability results in the expenditure of large research monies to develop a superior new cucumber inbred line.
The development of commercial cucumber hybrids requires the development of homozygous inbred lines, the crossing of these lines, and the evaluation of the crosses. Pedigree breeding and recurrent selection breeding methods are used to develop inbred lines from breeding populations. Breeding programs combine desirable traits from two or more inbred lines or various broad-based sources into breeding pools from which inbred lines are developed by selfing and selection of desired phenotypes. The new inbreds are crossed with other inbred lines and the hybrids from these crosses are evaluated to determine which have commercial potential.
Pedigree breeding is used commonly for the improvement of self-pollinating crops or inbred lines of cross-pollinating crops. Two parents that possess favorable, complementary traits are crossed to produce an F1. An F2 population is produced by selfing one or several F1""s or by intercrossing two F1""s (sib mating). Selection of the best individuals is usually begun in the F2 population; then, beginning in the F3, the best individuals in the best families are selected. Replicated testing of families, or hybrid combinations involving individuals of these families, often follows in the F4 generation to improve the effectiveness of selection for traits with low heritability. At an advanced stage of inbreeding (i.e., F6 and F7), the best lines or mixtures of phenotypically similar lines are tested for potential release as new cultivars.
Mass and recurrent selections can be used to improve populations of either self- or cross-pollinating crops. A genetically variable population of heterozygous individuals is either identified or created by intercrossing several different parents. The best plants are selected based on individual superiority, outstanding progeny, or excellent combining ability. The selected plants are intercrossed to produce a new population in which further cycles of selection are continued.
Backcross breeding has been used to transfer genes for a simply inherited, highly heritable trait into a desirable homozygous cultivar or inbred line that is the recurrent parent. The source of the trait to be transferred is called the donor parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent. After the initial cross, individuals possessing the phenotype of the donor parent are selected and repeatedly crossed (backcrossed) to the recurrent parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent.
Descriptions of other breeding methods that are commonly used for different traits and crops can be found in one of several reference books (e.g., xe2x80x9cPrinciples of Plant Breedingxe2x80x9d John Wiley and Son, pp. 115-161, 1960; Allard, 1960; Simmonds, 1979; Sneep et al., 1979; Fehr, 1987).
Proper testing should detect any major faults and establish the level of superiority or improvement over current cultivars. In addition to showing superior performance, there must be a demand for a new cultivar that is compatible with industry standards or which creates a new market. The introduction of a new cultivar will incur additional costs to the seed producer, the grower, processor and consumer; for special advertising and marketing, altered seed and commercial production practices, and new product utilization. The testing preceding release of a new cultivar should take into consideration research and development costs as well as technical superiority of the final cultivar. For seed-propagated cultivars, it must be feasible to produce seed easily and economically.
Once the inbreds that give the best hybrid performance have been identified, the hybrid seed can be reproduced indefinitely as long as homogeneity of the inbred parents is maintained. A single-cross hybrid is produced when two inbred lines are crossed to produce the F1 progeny.
Cucumber is an important and valuable field crop. Thus, a continuing goal of plant breeders is to develop stable, high yielding cucumber hybrids that are agronomically sound. The reasons for this goal are obviously to maximize the amount of fruit produced on the land used as well as to improve the fruit agronomic qualities. To accomplish this goal, the cucumber breeder must select and develop cucumber plants that have the traits that result in superior parental lines for producing hybrids.
According to the invention, there is provided a novel inbred cucumber line, designated 8D-5079. This invention thus relates to the seeds of inbred cucumber line 8D-5079, to the plants of inbred cucumber line 8D-5079 and to methods for producing a cucumber plant produced by crossing the inbred line 8D-5079 with itself or another cucumber line, and to methods for producing a cucumber plant containing in its genetic material one or more transgenes and to the transgenic cucumber plants produced by that method. This invention also relates to methods for producing other inbred cucumber lines derived from inbred cucumber line 8D-5079 and to the inbred cucumber lines derived by the use of those methods. This invention further relates to hybrid cucumber seeds and plants produced by crossing the inbred line 8D-5079 with another cucumber line.
Parts of the cucumber plant of the present invention are also provided, such as e.g., pollen obtained from an inbred plant and an ovule of the inbred plant.
In another aspect, the present invention provides regenerable cells for use in tissue culture of inbred cucumber plant 8D-5079. The tissue culture will preferably be capable of regenerating plants having the physiological and morphological characteristics of the foregoing inbred cucumber plant, and of regenerating plants having substantially the same genotype as the foregoing inbred cucumber plant. Preferably, the regenerable cells in such tissue cultures will be embryos, protoplasts, meristematic cells, callus, pollen, leaves, anthers, stems, petioles, roots, root tips, fruits, seeds, flowers or the like. Still further, the present invention provides cucumber plants regenerated from the tissue cultures of the invention.
Another objective of the invention is to provide methods for producing other inbred cucumber plants derived from inbred cucumber line 8D-5079. Inbred cucumber lines derived by the use of those methods are also part of the invention.
The invention also relates to methods for producing a cucumber plant containing in its genetic material one or more transgenes and to the transgenic cucumber plant produced by that method.
In another aspect, the present invention provides for single gene converted plants of 8D-5079. The single transferred gene may preferably be a dominant or recessive allele. Preferably, the single transferred gene will confer such trait as sex determination, herbicide resistance, insect resistance, resistance for bacterial, fungal, or viral disease, improved harvest characteristics, enhanced nutritional quality, improved agronomic quality. The single gene may be a naturally occurring cucumber gene or a transgene introduced through genetic engineering techniques.
The invention further provides methods for developing cucumber plants in a cucumber plant breeding program using plant breeding techniques including recurrent selection, backcrossing, pedigree breeding, restriction fragment length polymorphism enhanced selection, genetic marker enhanced selection and transformation. Marker loci such as restriction fragment polymorphisms or random amplified DNA have been published for many years and may be used for selection (See Pierce et al., HortScience (1990) 25:605-615, Wehner T., Cucurbit Genetics Cooperative Report, (1997) 20: 66-88 and Kennard et al., Theorical Applied Genetics (1994) 89:217-224). Seeds, cucumber plants, and parties thereof produced by such breeding methods are also part of the invention.
In the description and tables that follow, a number of terms are used. In order to provide a clear and consistent understanding of the specification and claims, including the scope to be given such terms, the following definitions are provided:
Allele. The allele is any of one or more alternative forms of a gene, all of which alleles relates to one trait or characteristic. In a diploid cell or organism, the two alleles of a given gene occupy corresponding loci on a pair of homologous chromosomes.
Backcrossing. Backcrossing is a process in which a breeder repeatedly crosses hybrid progeny back to one of the parents, for example, a first generation hybrid F1 with one of the parental genotype of the F1 hybrid.
Essentially all the physiological and morphological characteristics. A plant having essentially all the physiological and morphological characteristics means a plant having the physiological and morphological characteristics, except for the characteristics derived from the converted gene.
Regeneration. Regeneration refers to the development of a plant from tissue culture.
Single gene converted. Single gene converted or conversion plant refers to plants which are developed by a plant breeding technique called backcrossing wherein essentially all of the desired morphological and physiological characteristics of an inbred are recovered in addition to the single gene transferred into the inbred via the backcrossing technique or via genetic engineering.
Quantitative Trait Loci (QTL) Quantitative trait loci refer to genetic loci that control to some degree numerically representable traits that are usually continuously distributed.
Cavity. As used herein, cavity refers to the center of the cucumber fruit containing seeds and associated tissues.
Monoecious plant is said of a plant having separate staminate and pistillate flowers on the same plant.
Androecious plant: is said of a plant having staminate flowers only.
Gynoecious plant: is said of a plant having pistillate flowers only.
Yield: Fresh market cucumber yield is measured either in bushels, bins or cwt (hundredweight) per acre.
Blunt ends: Blunt ends are ends of the cucumber fruits that are not tapered or rounded.
Indeterminate vine or Indeterminate Growth: Refers to apical meristem producing an unrestricted number of lateral organs; characteristic of vegetative apical meristems. (Anatomy of Seed Plants, 2nd Edition, 1977, John Wiley and Sons, page 513). The main stem of the plant continues to grow as long as the plant stays healthy, as opposed to a determinate plant, which at some point in its life cycle will stop growing longer.
Fruit quality Fruit quality characteristics for slicing cucumbers include shape, length, skin color, firmness, interior characteristics and skin texture.
Extended yield pattern: A plant having an extended yield pattern will have a vine that will continue to produce fruit over a period of time, rather than producing all the fruits at once.
Blossom scar: The blossom scar is the small mark left on the distal end of the fruit after the flower falls off.
Blossom end: The blossom end is the distal end of the fruit (the xe2x80x9cfarxe2x80x9d end as measured from the base of the plant) where the flower blossom is located. The other end of a fruit is the stem end.
Reduced blossom end striping: Cucumber fruit normally have a striped pattern at the blossom end. The stripes are lighter color green or yellowish. 8D-5079 has a less distinct striping pattern than most other cucumbers.